Sam Rainsy, center, president of Cambodia National Rescue Party (CNRP) greets his supporters together with his party's Vice President Kem Sokha, on Rainsy's left, on his arrival at Phnom Penh International Airport in Phnom Penh, Cambodia, Friday, July 19, 2013. Thousands of cheering supporters greeted Cambodian opposition leader Sam Rainsy as he returned from self-imposed exile Friday to spearhead his party's election campaign against well-entrenched Prime Minister Hun Sen. (AP Photo/Heng Sinith)

"I have come home to rescue the country," Rainsy told the crowd gathered at Phnom Penh's airport, after kneeling to kiss the ground.

"I am happy to be here!" Rainsy shouted to be heard through a microphone as the supporters chanted, "We want change!"

The French-educated leader of the Cambodia National Rescue Party has been in exile since 2009 to avoid serving 11 years in prison on charges many consider politically motivated.

Rainsy, 64, received a royal pardon last week at the request of Hun Sen, his bitter rival whose ruling party is almost certain to maintain its ironclad grip on power in the July 28 general election.

Hun Sen has ruled for 28 years, and his party has 90 of the 123 seats in the National Assembly. The prime minister recently said that he intends to stay in office until he is 74 — cutting back from an earlier vow to stay in control until he's 90.

Critics of the government claim the election will be neither free nor fair, arguing that Hun Sen's regime manipulates the levers of government and influences the judiciary to weaken the opposition.

Last month, 28 opposition lawmakers were expelled from parliament when a committee run by Hun Sen's party ruled they had broken the law because they had originally won their seats in the name of the Sam Rainsy Party, but were campaigning under the recently established Cambodia National Rescue Party, into which it was merged.

They can still run in the upcoming election, but without parliamentary immunity. Immunity from arrest is a great benefit in Cambodia's elections, and those without it are at risk of being charged with defamation for remarks seen critical of Hun Sen and his government.

Rainsy is a charismatic and fiery speaker — qualities that have landed him in trouble before.